1. Field of the Invention
The invention relates to an electric direct current machine.
2. Description of the Related Art
An electric direct current collector machine, which can be used as a motor as well as a generator, is known (for example, from DE 33 24 617 A1). For this collector machine, a rotor, carrying a plurality of non-ferrous coils of electrical conductors at uniform angular intervals on the same diameter, is rotatably mounted in one housing. On the inner sides of the end surface of the housing, rigidly disposed permanent magnets of polarity, differing consecutively in the circumferential direction, are located opposite to and on either side of the coils. The conductors, forming the coils, are connected in turn to commutator contact surfaces, which rotate with the rotor and are insulated electrically from one another and on which sliding contacts, which are provided in the housing and insulated from the wall of the housing and which are connected conductively with external electrical connections, are pressed. When connected to an electric direct current source, the machines, so constructed, act as a motor. On the other hand, when the rotor shaft is driven, they act as a generator, that is, electrical direct current can be collected from their terminals. These known direct current machines find use, for example, as small, very compact motors of low output, for example, as motors for driving recording devices for video signals. Because of the special arrangement of the rotor coils and the permanent magnets and the therefrom resulting course of the interacting fields of the permanent magnets and the rotor coils, such motors are also referred to as axial field machines. Because of the good efficiencies that can be attained with them and because of the basically good possibilities of regulating them, such axial field machines, with larger dimensions and a correspondingly higher output, have also been proposed, for example, as driving motors for vehicles (WO 95/17779).